Optimize daysSince2000

10% performance improvement in https://scratch.mit.edu/projects/527835108/

src/compiler/jsexecute.js

@@ -330,21 +330,14 @@ const timer = () => {
     return t;
 };
 
-// This is the "epoch" for the daysSince2000() function.
-// Storing this in a variable is faster than constantly recreating it.
-const daysSince2000Epoch = new Date(2000, 0, 1);
-
 /**
  * Returns the amount of days since January 1st, 2000.
  * @returns {number} Days since 2000.
  */
-const daysSince2000 = () => {
-    const today = new Date();
-    const dstAdjust = today.getTimezoneOffset() - daysSince2000Epoch.getTimezoneOffset();
-    let mSecsSinceStart = today.valueOf() - daysSince2000Epoch.valueOf();
-    mSecsSinceStart += ((today.getTimezoneOffset() - dstAdjust) * 60 * 1000);
-    return mSecsSinceStart / (24 * 60 * 60 * 1000);
-};
+const daysSince2000 = () =>
+    // Date.UTC(2000, 0, 1) === 946684800000
+    // Hardcoding it is marginally faster
+    (Date.now() - 946684800000) / (24 * 60 * 60 * 1000);
 
 /**
  * Determine distance to a sprite or point.